1. Field of the Invention
This invention relates to reverse flow cooled dynamoelectric machines and more specifically to an improved arrangement for cooling the rotor and stator of such machine.
2. Description of the Prior Art
Dynamoelectric machines, such as large turbine-generators, typically are cooled by a gas such as hydrogen flowing through the interior of the rotor, through the gas gap between the rotor and the stator, and through the stator laminations. The stator windings may or may not be additionally cooled by a liquid flowing within the windings themselves. In the past, the most effective way of cooling a dynamoelectric machine was considered to be pumping gas directly from gas coolers to the end regions of the stator by a fan mounted on the generator rotor. This cooling scheme, of pumping cooling gas from a gas cooler across end regions of the stator core, through the stator and thereafter back to the gas cooler is known as forward flow ventilation. However, as the ratings of large turbine-generators increased, it was found that a heating problem in the end regions of the generator rotors became a limiting factor of the capability of these machines. In order to cool these localized areas of excessive heating in the generator rotors, a reverse flow cooling scheme was adopted wherein cooling gas was pumped by the fan toward two separate gas coolers, the flow being divided upstream from the coolers, a portion of it being pumped through a first cooler and then into the end turn region of the rotor to cool this region and the remainder of the gas being pumped through a second cooler and then through the cooling passages of the stator core and the body portion of the rotor. Such a reverse flow ventilation scheme is shown in U.S. Pat. No. 3,739,208 to Shartrand, assigned to the assignee of the present invention.
In such a cooling arrangement, shoud one of the coolers become inoperative, the associated portion of the dynamoelectric machine may not receive any cooled gas from that cooler. Therefore, should one of the coolers fail to operate either the stator laminations and rotor body or the rotor end turn region will receive no cooled gas at all. However, it is required that should one of the coolers fail to operate, the dynamoelectric machine remains operational at a reduced load. Starving either the stator laminations and rotor body or the rotor end turn region from cooled gas severely limits the reduced load capabilities of the dynamoelectric machine should one of the coolers fail to operate.
As the ratings of dynamoelectric machines increase, the machines themselves become physically larger. Modern turbine-generators are of a size which makes them extremely difficult to ship, requiring special means of transportation. To minimize the difficulties of transporting large dynamoelectric machines and to minimize the cost of this transportation, dynamoelectric machines have been constructed with removable gas coolers disposed within removable domes located at the ends of the dynamoelectric machines radially outwardly from the machine casing. However, some dome constructions such as that shown in U.S. Pat. No. 3,652,881 to Albright et al and U.S. Pat. No. 3,833,826 to Barton et al, assigned to the assignees of the present invention, have heretofore been used only with forward flow dynamoelectric machines.
In prior art reverse flow cooled dynamoelectric machines the high pressure and flow developed by the fan effectively cools the end turn portions of the rotors, eliminating these portions as areas limiting the output capabilities of the machines, and the thermal performance of the body portion of the dynamoelectric machine rotors has become a limiting factor in the output capabilities of the machine.
By the present invention, the above difficulties and disadvantages associated with the prior art are avoided and an approach is provided in which an improved arrangement of duplex gas coolers disposed in a removable dome and uniquely baffled allows both the body portion and the end turn portion of the rotor to be effectively cooled while also effectively cooling the stator of the machine even when the machine is operated at a reduced load due to the inoperability of one of the coolers.
Accordingly, it is an object of the present invention to provide a reverse flow cooled dynamoelectric machine wherein both the stator and the rotor are effectively cooled under reduced load conditions when one of the gas coolers employed in the machine is operative.
It is another object of the present invention to provide a reverse flow cooled dynamoelectric machine which provides improved thermal capability in the body portion of the dynamoelectric machine rotor under normal operation.